Philosophy Discussion Forums

sciencedaily.com/releases/2012/11/12111 ... 135516.htm

A common theme in discussions about human evolution is the idea that comfortable modern lives, and particularly modern medicine have reduced or removed selective pressure.

The interesting thing about the findings discussed in the article to which I've linked above is that they suggest this could have happened earlier than we might think and that the selective pressure - the hardship and death - required to cause us to evolve our intelligence is, by any even remotely modern standards, massive.

The result seems to be that it isn't just the modern medicine of the past 100 years or so that has eased off the pressure enough to stop it from being effective. It's the entire development of complex human societies. Recorded human history, by definition, tends to go back only as far as the development of societies sophisticated enough to leave detailed records. But, it seems, the very act of reaching that level of sophistication is enough to reduce the pressure sufficiently to "turn off" evolution.

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The most interesting thing to me is what, if anything, this might say about evolved human psychology and how it works, or doesn't work, in modern (i.e. no more than a few thousand years old) societies. The research seems to show even more than ever before that failure and death are much, much more "the norm" than success and life.

The findings re-iterate even more the contrast between our modern relatively threat-free lifestyles and the lives that our pre-historic ancestors must have lived. Perhaps it goes some way to explaining our constant need to create threats where none need exist.

Finally, the phenomenon of paint-balling is explained.

To ask, how do you define evolution as people differ on what it means?

PhilX

I mean the adaptation, over many generations, of a species to its environment by selective pressure acting on inherited characteristics that are subject to small random variations.

Human evolution has not stopped.

And it will never stop.

The human genome (like all others) is inherently unstable, there are subtle changes from one generation to the next. The changes may be small and not discernible from one generation to the next, But over a thousand or more generations there will inevitably be changes, especially when the environment is changing as fast as it is in the current century.

That's why I put the word stopped in scare-quotes.

I don't mean it literally. I'm talking about a reduction in selective pressure.

Steve3007 wrote:That's why I put the word stopped in scare-quotes.

I don't mean it literally. I'm talking about a reduction in selective pressure.

Selective pressure is only reduced when the environment is static, or effectively static.

I would say that the human environment is changing faster than it has ever done before. There is no reduction in selective pressure.

Yes selective pressure is reduced if the species has already adapted to the environment and the environment is not changing significantly.

But it's also reduced if the environment has effectively been removed and replaced with a controlled-environment that can itself be adapted to the species. That, I think, is what human societies do. We've made our "environment" adapt to us, rather than the other way around. In this case, I guess the environment is artificially kept relatively static. i.e. it tracks us.

What would you say are the selective pressures in human societies? What do you think are the main factors that stop people from passing on their genes successfully?

What do you think are the main factors that stop people from passing on their genes successfully?

Ugliness.

[quote="Steve3007"]Yes selective pressure is reduced if the species has already adapted to the environment and the environment is not changing significantly.

But it's also reduced if the environment has effectively been removed and replaced with a controlled-environment that can itself be adapted to the species. That, I think, is what human societies do. We've made our "environment" adapt to us, rather than the other way around. In this case, I guess the environment is artificially kept relatively static. i.e. it tracks us.

Interesting. Can you give an example of the environment adapting to humans?

Misty: What I meant was that we adapt our environment to suit our needs. That is the sense in which I meant that the environment tracks us and thereby stays constant relative to us.

An example: the environment between my skin and my clothing. In winter, at least, it's artificially warm compared to the "natural" environment outside, and thereby saves the need for me to die of cold and stop passing on to my children my inability to deal with cold using only the body that Nature gave me.

An example that's more relevant to the "stopping" of the evolution of our mental capacities that is discussed in the article cited in the OP:

As we've developed large complex human societies we've all but eliminated predators from our environments. So we don't have the need for constant watchfulness and alertness to danger that our ancestors must have had.

Rederic:

Ugliness.

You've obviously never walked through the middle of Chatham (Kent, England) just after chucking out time on a Saturday night.

A_Seagull wrote:Selective pressure is only reduced when the environment is static, or effectively static.

I would say that the human environment is changing faster than it has ever done before. There is no reduction in selective pressure.

Regardless of how you define and measure environmental change, selective pressure only increases when the rate of survival or fecundity decreases. So by some definitions environmental change could be massive, but unless it's associated with a significant fall in birth rate, most commonly by lots of people dying, those changes wouldn't affect selective pressure much. If everybody lives their full span, genes get passed on without tending in any direction, except for differences in procreation rates.

And the bigger and more homogeneous the world's population, the slower the changes in phenotype (observable characteristics). Evolution in terms of genetic mutations proceed at a normal pace, but people don't change much. Someone with severe disabilities that would have been fatal in hunter gatherer times today gets treated and lives long enough to beget children. But if you have a plague that wipes out half the population, that's when you'd see significant changes in disease resistance and other characteristics. If that plague killed 90% of us, you'd see bigger changes. If it killed all but 10,000 people, the next generation would be even more different.

Why do the races - European, African, Asian - look so different? Small numbers, reproductively isolated in Europe and Asia from Africa. What they call the founder effect - the small number of individuals who reached Asia and Europe would have had, by chance, different physical, facial, intellectual, and emotional characteristics from the average back home in Africa. Those in Asia would have had, by chance, different characteristic than those in Europe. And of course life was very dangerous for the pioneers, so any characteristics that offered survival advantages would be snapped up by evolution.

So selective pressure today is awfully small. The only direction for phenotype changes nowadays is toward the characteristics of those people who are having more children - the poor and undereducated. Selective pressure by survival advantage is almost nil in the developed countries.

Selective pressure by survival advantage is almost nil in the developed countries.

Yes, and that has been the subject of previous threads in this forum. The thing that I found interesting in the article to which I placed a link in the OP is the suggestion that this selective pressure has not just eased off with the advent of modern technological societies and modern medicine, but that it started easing off as soon as the first sophisticated societies started to emerge several thousand years ago.

Steve3007 wrote:

Selective pressure by survival advantage is almost nil in the developed countries.

Yes, and that has been the subject of previous threads in this forum. The thing that I found interesting in the article to which I placed a link in the OP is the suggestion that this selective pressure has not just eased off with the advent of modern technological societies and modern medicine, but that it started easing off as soon as the first sophisticated societies started to emerge several thousand years ago.

I'm sure that's true, especially as societies grew larger in numbers.

Wilson wrote:

A_Seagull wrote:Selective pressure is only reduced when the environment is static, or effectively static.

I would say that the human environment is changing faster than it has ever done before. There is no reduction in selective pressure.

Regardless of how you define and measure environmental change, selective pressure only increases when the rate of survival or fecundity decreases. So by some definitions environmental change could be massive, but unless it's associated with a significant fall in birth rate, most commonly by lots of people dying, those changes wouldn't affect selective pressure much. If everybody lives their full span, genes get passed on without tending in any direction, except for differences in procreation rates.

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Do you not know much about the history of the 20th century? Large sections of the human population failed to procreate through war, famine and disease, to mention but a few causes. (Or to mention a few specific cases WW1, WW2. 1919 flu epidemic, Stalin's purges, Chinese famine in 60's.)

The human environment has changed greatly over the past 1000 years and is still changing very fast. It requires different skills to survive and procreate efficiently in different environments. And so I suspect evolution is happening faster then ever.

The progress of evolution cannot be measured over a few generations, it would take about 1000 generations to detect any significant trend. So just because there have been no major differentiation in breeding success between peoples over the past 20 years is no evidence that evolution has stopped, nor even that it is slowing down!

A thousand human generations is almost 20,000 years. We've been somewhat civilized for about 3000 years. Back in hunter gatherer days survival was tenuous - food shortages, disease, accidents, poorly protected from the elements, warfare between tribes, animal predators, and so on. When you have the entire human population at risk of dying on a constant basis, evolutionary change in the phenotype had to be a lot faster than today, when in large segments of the globe, life is relatively risk free. It's easy to look at the news and think that the world has never been this chaotic before - but trust me, our ancestors would marvel at the stability and safety of today.

As I said before, the poor and disadvantaged of the world are procreating faster than those who are well off, and that will cause some change in humanity, on average. What that means as to a shift in average personality and intelligence in the coming generation, I don't know; probably not that much.